1. Field of the Invention
The present invention relates to an endoscope apparatus, more particularly, a constitution used in medical fields for forming and displaying a spectral image (video) made up of image information of arbitrarily selected wavelength ranges.
2. Description of the Related Art
Recently, in a electronic endoscope apparatus which uses a solid imaging device, spectral imaging combined with a narrow band pass filter on the basis of a spectral reflectance in alimentary canal (gastric mucosa and the like), namely, a narrow band filter built-in an electronic endoscope apparatus (Narrow Band Imaging-NBI) has become the focus of attention. In place of rotational filters of R (red), G (green) and B (blue) by a frame sequential method, this system is provided with band pass filters of three narrow bands (wavelengths), outputs sequentially illumination light via these narrow bandpass filters, and conducts processing the same as in the case of red (R), green (G) and blue (B) signals while changing respective weightings to three signals obtained from these illumination lights, thereby forming a spectral image. This spectral image is able to realize micro-structures and the like in gastrointestinal tracts such as the stomach and large intestine, which would otherwise not be realized.
In contrast, unlike the frame sequential method using the above-described narrow band pass filters, as described in Japanese Published Unexamined Patent Application No. 2003-93336, it has been proposed that in the simultaneous method in which micro-mosaic color filters are arranged on a solid imaging device, a spectral image is formed by the computing process on the basis of image signals obtained from white light. In this method, the relationship between numeric data of the respective R, G, and B color sensitivity characteristics and numeric data of spectral characteristics of a specific narrow bandpass is determined as matrix data (coefficient sets) and computing is made for the matrix data and the R, G and B signals to obtain spectral image signals artificially via the narrow bandpass filters. Where a spectral image is formed by such computing, it is not necessary to provide a plurality of filters corresponding to desired wavelength ranges and to provide these change-over arrangements, thereby successfully avoiding increases in the size of a system and reducing cost.
However, in forming a spectral image by the endoscope apparatus, underlying color image signals are R (red), G (green) and B (blue) signals. When a solid imaging device is used, for example, a complementary color-type CCD having color filters Mg, Ye, Cy and G, Mg (magenta), Ye (yellow), Cy (cyan), and G (green) signals are often converted to a brightness (Y) signal and a color difference (C) signal (Y/C signals) for processing. Also, the Y/C signals must be subjected to color conversion to RGB signals. Further, where an elementary color-type CCD having RGB color filters is used, RGB signals are converted to Y/C signals due to matters related to a variety of signal processings and circuit configurations at subsequent steps. In this case, it is necessary to make RGB signals from Y/C signals. Such color conversion processings are in principle redundant, and such a problem is brought about whereby repeated color conversion may cause deterioration in quality of images and complicate the circuit configuration.
On the other hand, recently, endoscope apparatuses in which different types of endoscopes (scope) are connected to a single endoscope have been used. In this case, Y/C signals or RGB signals are outputted from the endoscope, and a spectral image may not be formed depending on output formats of the endoscope. Therefore, user-friendly endoscope apparatuses have been demanded in view of such circumstances.